Process and mechanism for the operating of a rolling mill

ABSTRACT

The disclosure of this invention relates to a method and apparatus for operating a tandem rolling mill, wherein one or more of the stands thereof can be operated as a soft stand in order to reduce the workpiece more or less uniformly across its width to aid in entrance of the front end of the strip into the next stand or coil forming reel, after which the stand can be converted to a hard stand to roll to a desired gauge.

United States Patent [191 Bald Jan.1,1l974 [75] Inventor:

[ PROCESS AND MECHANISM FOR THE OPERATING OF A ROLLING MILL WilfriedBald, l-lilchenbach-Dahlbruch, Germany [73] Assignee: Siemag SiegenerMaschinenbau,

Gmbll, Hilchembach-Dahlbruch, Germany [22] Filed: Mar. 27, 1972 [211Appl. No.: 238,032

[30] Foreign Application Priority Data Mar. 30, 1971 Germany P 21 15344.6

[52] US. Cl. 72/14, 72/20 [51] Int. Cl 1321b 37/00 [581 Field of Search72/8, 9, 10, 11, 72/19, 21, 245, 14

[56] References Cited UNITED STATES PATENTS 3,157,073 11/1964 Blain72/245 3,464,245 9/1969 Dowsing et a1. 72/16 3,470,722 lO/l969 Woodcocket al.... 72/237 3,204,441 9/1965 Lyle .1 72/231 3,491,562 1/1970Kajiwara 72/12 Primary Examiner-Milton S. Mehr Att0rneyHenry C. Westin57] ABSTRACT The disclosure of this invention relates to a method andapparatus for operating a tandem rolling mill, wherein one or more ofthe stands thereof can be operated as a soft stand in order to reducethe workpiece more or less uniformly across its width to aid in entranceof the front end of the strip into the next stand or coil forming reel,after which the stand can be converted to a hard stand to roll to adesired gauge.

8 Claims, 4 Drawing Figures M) i i PATENTEDJAH 1 1914 3382 5155 sum 10?a Fig.1" (6 g g I Fig.3

PROCESS AND MECHANISM FOR THE OPERATING OF A ROLLING MILL The inventionrefers to a process for the operation of a rolling mill stand and/or amill train formed by several rolling mill stands as well as a mechanismfor the execution of the process. The invention refers especially to aprocess, as well as a mechanism, for the alleviation of the frequentdifficulties in the entrance of the leading end of a strip, especiallyrolled steel strip into the stands, and the frequent difficultiesexperienced in the strip leaving the stand or stands.

In order to obtain close tolerances of rolled stock, it is known toequip single stands or one or more of the several stands of mill trainswith regulating systems for the adjustment of the roll gap, by means ofwhich an adjustment of the rolled stock is effected to obtain constantgauge. For common, non-regulated stands, and especially for regulatedstands, it turned out that special problems occur at the initial pass ofa rolled stock. The greatest problems result at the initial pass of arolled stock when the stock is asymmetrical in crosssection. In the caseof a strip entering the roll gap with a slight trapezoidal profile, thestrip is stretched to a greater extent on its thicker side while passingthrough the roll gap, so that it approaches the following unit, whichcould either be a stand or a coiling device, in the shape of a circularare being slightly laterally bent.

Due to this deviation from the desired rolling axis, the strip does notstay within the prescribed path of travel. Instead, the strip tends tomove laterally in which its edge is forced against adjacent stationaryequipment causing it to buckle requiring that the rolling operation beinterrupted and and the strip be removed. It is true that the next standor coiling device is generally preceded by lateral guides, but theguides cannot on the tendency of the lateral displacement of the stripaway from the rolling axis correct the advancing rolled stock to centerit in the direction of the rolling axis. The purpose of the guides israther to lead the end issuing from the stand and to advance it alongthe rolling axis to the next stand or coiling device. In a number ofcases, the leading end of the rolled stock is therefore not picked upcorrectly or not picked up at all by the next stand or coiling device,so that the stand must be shut down until the stock is removed.

The present invention has for its object a method for the operation of arolling mill stand, in which, after a strip enters the pass, the rollscan adapt themselves to the actual profile of the strip in which thestrip is engaged above its entire width and, accordingly, is stretchedto the same extent over its width so that it can be advanced above adesired rolling axis.

This is attained with roll stands of the described type in that from apoint of time, which lies between the delivery of a strip from a standand the entry of the next strip into this stand, a regulating mechanismassigned to the stand is operated during a given period of the advanceof the leading end of the next strip to effect an increase of theswelling or stretch of the stand. Due to the increase of the standswelling which corresponds to a decrease of the stand modulus, there isattained a more uniform-reduction of the profile and, connectedtherewith, a more uniform stretching of the rolled strip independent ofthe fact that the strip entering the stand may not have a rectangularprofile. The leading end of the strip leaving the stand is thus keptfrom laterally bending, i.e., tending to take a ring sectional shapecondition by asymmetrical stretching, and advances straight andsymmetrically in the direction towards the next stand or coiling device.

The period of advance of the strip leading end with the decreased standmodulus condition can be determined to be a specified time interval ofthe period of advance. In one form arrangements can be made to terminatethe time interval for the advance of the leading end of the strip assoon as it entered the next stand, or a coiling device. In anotherarrangement the time interval of the advance of the leading end can bemade to terminate upon the building up of a tension in the stripdelivered by the roll stand because such tension is a very definite signof the reception of the leading end of the strip by the next unit.

For the practice of the method of the present invention it has provenadvantageous to utilize stands whose housings are equipped with acontrol means and a means for adjusting the rolls as well asestablishing a given stand modulus. In accordance with the invention,the control means include a switching means which makes effective one ofat least two variable values of stand modulus. Sensors are also includedwhich monitor the delivery of strip as well as its entry and whichdetermine the operating position of the switching means.

The sensor may take the form of a feeler roll arranged with itsperiphery projecting into the path of the rolled stock with a lowcontact angle between the roll and the underside of the strip andadapted to be rotated by the passing strip; thereby monitoring thepassing strip. The feeler roll may be supported by a pressure cellacting as a sensor, or the feeler roll may be assigned to a switchoperated by its movement, for example, the angle of traverse of a leversupporting the roll. Further, light barriers can be employed as sensorsto monitor the path of the strip and in many cases there can be utilizedinstead of the light barrier a simple photoelectric cell reacting to redor infrared light responsive to passing red-hot strip. Furthermore, thesensor can be constructed as electrical measuring and/or controllingdevices, which may be located in the armature current circuits of thedrive motors for the stands and which allow for the detection of theentry of the rolled strip as well as the building up of tension thereinas a function of variations of the armature current. Also, pressurecells associated with the housings can be utilized as sensors and beconnected to one or more switching mechanisms.

Sensors can act directly upon the switching device so that throughactivating one or two sensors there can be effected a two-positionoperation of the switch device. For this, there can be provided separatesensors for operating the switching device as well as for a resettingmechanism therefor, and it may be desirable to connect only one sensorwith the switching mechanism and to determine its switching position inaccordance with its own activation. As an example, when utilizing feelerrolls it can be brought about that the higher stand modulus is onlyeffective if a passing strip is under tension, so that the entry as wellas the delivery of the strip is effected at a preselected stand modulus.With the utilization of two sensors, the loading or release of one ofthem can effect the switching and that of the other, can effect thereverse switching. In case of emergency the effect of one of thesensors, preferably that for the reverse switching, can be givenprominence. On the other hand, it is possible to provide timing relaysbetween the sensor and the switching mechanism which transmit anoperating signal on a delayed basis so that the required time can begiven to allow the building up of the strip tension, especially for thelast stand of a mill train, at which interval the housing modulus is tobe changed after the entry of a strip. In this case the sensor candetermine the moment of switching of the switching mechanism; and thesame operating signal belonging to it can effect reverse switching,delayed by means of a timing circuit. Such timing circuits can also beprovided for the bridging of the path differences of other stands.

Sensors can also be utilized, especially in mill trains, for theactivating of the switching mechanisms of two stands, i.e., of apreceding as well as of a following stand; thus, the switching processcan be effected by means of one of the sensors assigned to the precedingstand and the reverse switching can be effected through activating oneof the sensors of the following stand.

Generally, the expenditures can be reduced ifa common switchingmechanism is assigned to each controlling device of the housings of astand. In one form the switching mechanism, during the period of advanceof the leading end of the strip, separate control mechanisms areconnected with separate housing pressure measuring devices and receive adifferent load signal. In this case, subsequent to the reverse switchingof the switching mechanisms, the separate control mechanisms of ahousing receive signals of the same actual value of the load, which isdetermined through the formation of the sums of the loads of thepressure cells of both housings.

The above features and advantages of the present invention will bebetter understood when the following description is read along with theaccompanying drawings, of which:

FIG. I is a schematic view ofa six-stand tandem train incorporating thefeatures of the present invention;

FIG. 2 is a schematic view of one of the four-high stands of the tandemtrain shown in FIG. 1 with mechanical and hydraulic screwdown devicesrepresented in the form of block diagrams as well as control deviceassigned to the latter;

FIG. 3 is a schematic sectional view cut through a strip passing betweenthe working rolls of a stand; and

FIG. 4 is a second block diagram of dual control devices with separateswitching devices associated with them.

FIG. 1 shows schematically a tandem train with six four-high stands I to6. It is customary for the reducing of the tolerances of the rolledstrip by the tandem train to operate stands of such trains with controldevices in order to increase the stand modulus and, thereby, therigidity of the stands.

FIG. 2 shows as an enlarged representation one of two identical housingsof stand 1 of FIG. 1. The working rolls 7 and 8 form between them a rollgap 9 and are supported by backing rolls 10 and 11 whose lower chocksrest upon mechanical screwdown mechanisms formed by adjustable wedges12; whereas, the upper chock is subject by being in contact with afiller plate 13 to the force of a hydraulic cylinder provided as ahydraulic screwdown mechanism 14.

The operating pressure of the hydraulic cylinder 14 is effected by meansofa control device 15; FIG. 2 illustrating only the device for one ofthe two housings of the roll stand 1. The corresponding load of thestand results from the pressure occurring in the hydraulic cylinder. Thepressure is fed by piping 16 to a pressure transformer 17 which suppliesto the pressure analagous values of the control device 15. Associatedwith the control device 15 there is a servovalve 18, which connects theline 16 with a pressure line 19 and a return line 20. The return line 20returns the pressure medium, such as, oil supplied to it, to a supplysump wherefrom it is carried into a pressure reservoir by means of apressure pump. This reservoir feeds the pressure line 19. By thisarrangement it is possible by connecting the line 16 with the returnline 20 to reduce the amount of the pressure medium in the hydrauliccylinder 14, while pressure medium can be fed into the hydrauliccylinder by connecting the line 16 with the pressure line 19.

For the adjustment of the desired roll gap, the control device isprovided with a setting means 21 for the desired opening of the roll gapand the actually resulting roll gap is controlled by the actual-valueindicator 22. Such actual-value indicators, e.g., constructed astranductors, can be assigned to the chocks of the rolls or, as in theform of the construction illustrated, to the hydraulic cylinder 14itself. But, it is also possible to provide a monitor 23 as anactual-value indicator or additionally to another actual-valueindicator, which controls the gauge of the delivered roll strip.

The regulating characteristic is determined by two indicators 24 and 25,each of which is connected to the control device 15 by means of aswitching mechanism 26. The specific switching position of the switchingmechanism 26 is determined by sensors associated with it. In the form ofthe construction illustrated there are provided as sensors aphotoelectric cell 27 reacting to red or infrared light, as well as apressure cell 29 activated by a feeler roll 28, the cell and roll beinglocated in the path of travel of the strip.

Before the commencing of the rolling operation, the adjustable portionsof the wedges 12 of the stands I to 6 are shifted in such a manner thatthe tops of the lower working rolls are brought to a predeterminedpassline. In now referring to only one of the stands, through anadequate selection of filler plates 13, which are kept on hand indifferent thicknesses, it can be assured that during rolling thehydraulic cylinders 14 will remain within their desired working rangewhich, in this case, can be chosen relatively narrow. Now, the rolls canbe subject by means of the line 16 to a pressure which corresponds withthe anticipated rolling force. The latter is sent to the correspondingcontrol devices 15 by means of an adjustable selsyn 30. In this way,during the slow rotating of the rolls, the working rolls can be pressedstrongly against each other and the position indicator 22, in the form,for example of the abovementioned transductors, can be set, i.e.,adjusted to a zero setting. Subsequently, the hydraulic cylinders 14will be un-loaded so as to position the upper rolls in the unloadedcondition that will produce the desired roll gaps when the strip entersthe stands and the housings stretch under the rolling loads.

If now a roll strip, eg a hot strip, is fed to a mill, for example,stand 1, the indicator 24 is first made active by means of the switchingmechanism 26; thus causing the control device 15, pursuant to itsregulating characteristic, to set the initial desired stand modulusthrough operation of the cylinders 14. This initial stand modu- [us isof such a nature that the natural rigidity of the stand is not increasedby the control device as normally would happen, but, instead, it israther considerably decreased. Thus, there is practically effected anegative" adjustment in which for an increasing rolling force oil isallowed to escape the hydraulic cylinders; whereas, the cylinders aresupplied with oil under a decreasing rolling force. Such a yieldingstand allows, firstly, a more gently entry of the strip into the rollgap. But more importantly, it provides that the entry of the strip isimproved considerably in the event, as shown in FIG. 3 the profile ofthe strip 31 is not exactly rectangular, but, for example, somewhattrapezoidal.

ln customary roll stands, due to the rigidity or the high stand modulus,the thickness of such strip is not reduced proportionally to thestrength distribution over the width or, at least, over a constant valueover the width; but the trapezoidal profile is rolled down to a more orless rectangular one, so that there is effected an increased lengtheningof the original thicker side of the strip. The strip delivered from theroll gap is therefore more lengthened on the original thicker side thanon the opposite side, which slightly bends the strip in a ring-likeshape. Consequently, the strip is laterally displaced from the verticalplane of symmetry of the mill train and with a curvature so that thereexists the dangerthat it may not enter the next stand, but instead,piles up between the stands requiring with much effort that it beremoved. This can be avoided by means of the control devices 15, due tothe low stand modulus attained through the activity of the selsyn 30,the natural rigidity of the stand is not, as customary for roll gapadjustments, increased; but rather considerably decreased so that therolls 7 and 8 can adapt themselves to the profile of the roll strip 3].ln this event the advance of the strip is effected by means of theengagement of the rolls over the entire width and, simultaneously, thestrip is reduced over the entire width by an equal amount or an amountproportional to the respective thickness or in amounts lying betweenthese two conditions, so that the tendency for the formation of a ringsection shape does not exist. Thus, the strip will take a straightcourse and will not deviate from the vertical plane of symmetry of thetandem train, so that it will reach the next stand safely and in asymmetrical predetermined position.

During the advancement of the strip, subsequent to leaving a stand, itpasses over the feeler roll 28 located immediately after the stand.Because this feeler roll reaches only slightly into the path of thestrip, it is passed over and, after having passed the feeler roll, theleading end of the strip lowers itself in the direction of the guides ofthe following stand. Only when the leading end of the strip is caughtsecurely by the rolls of the following stand, will there occur a tensionin the strip between both stands, which due to the engagement of thefeeler roll even with only a low circumferential angle, placing a loadon its supporting element. This load, when absorbed by the pressure cell29, will cause the cell to produce a signal which is fed to theswitching mechanism 26 and which effects operation of the switchingmechanism. As aresult, the indicator 24 is disconnected from the controldevice of FIG. 2 and the indicator 25 will be connected with it. Theindicator 25 is adjusted to another rigidity and effects a considerablydifferent stand modulus than indicator 24. The normal rigidity of thestands is now increased to the extent as required by the gaugeadjustment of the strip during the rolling operation. Special concernabout the entry of the succeeding portion of the strip, especially thepossibility of the off-track feeding of strip whose profile deviatesfrom the rectangular shape, no longer has to be considered because theleading end of the strip will have been gripped by the next stand tosubject the strip to a guiding tension.

in relating the invention to a tandem train, let it be assumed that acold strip is to be rolled. The stands 1 to 6 are similarly constructedand also present the same delivery stand modulus of approximately 550ton/mm., that is to say, an increase of the rolling force ofapproximately 550 tons results in an expansion or stretch of 1 mm.During the entry of the strip under the influence of the indicator 24,each of the stands will be brought to a reduced stand modulus of 50ton/mm; thus, the stands are brought to approximately one tenth of theirnormal rigidity due to the adjustment. After the correspondingadvancement of the leading end of the strip, the switching mechanisms 26are activated, which disconnect the indicators 24 and connect theindicators 25. Consequently, the stands again receive a higher rigidity.It may be desirable to use an extreme rigidity corresponding to a highstand modulus in the present form of construction only for the stands 1and 2. In this case stands 3, 4 and 5 can be adjusted to magnitudeswhich correspond to the normal stand modulus which is established by themechanical stiffness of the mill, that is to say, the modulus of asimilar stand without a control device. The last stand 6 can be broughtto a stand modulus corresponding to approximately onehalf of the normalstand modulus.

The invention is not limited to cold rolling nor the utilization of sixstands. Among others, it can be applied to hot mills, cold mills anddouble cold reduction mills as well as to individual stands. Theapplication of the invention is also not dependent of the type ofadjustment. It can be utilized in combination with the customary, purelymechanical adjustments in which the corresponding stand load isestablished only by pressure cells. Disadvantages to be observed in suchadjustment devices and control mechanisms are found in their slowresponse time in effecting a roll gap adjustment.

Correspondingly, the controlling mechanism itself can be altered. in theform of construction illustrated, the desired roll gap is established bya setting means 21 and the actually adjusted roll gap is controlled by amonitor 23, which is located after the stand and gives the actual valueof the roll gap. In the described setting process, the positionindicators 22 are adjusted to the zero position upon the pressurizationof the hydraulic cylinders 14. Such position indicators can be locatedbetween the checks, if desired. In the form of construction shown in thedrawing the position indicators 22 are assigned to the hydrauliccylinders 14 and, adjusted in the initial position in which they notonly indicate the movement of the pistons relative to the hydrauliccylinders, but, simultaneously, also the position of the rolls and serveas an indicator of actual value of the roll gap.

The time of switching of the switching mechanism 26 can also be altered.Thus, at the delivery of a strip from a stand, the stand can beconverted to the soft or low stand modulus condition by the switchingmechanism 26 activating the indicator 24. Such switching over at orshortly after the unloading of the preceding stand avoids the tendencyof a lateral deviation of the tail end of the strip. In the same mannerit is also possible to switch over the stands simultaneously to thelower of the modulus of both stands, but only after the delivery of therolled stock from the train. to assure effective grasping of the leadingend of the strip in the stand, it can be advantageous to effect theswitching over only at the moment the leading end of the strip entersthe roll gap. The stand will continue to operate at the low moduluscondition only during the subsequent short interval, which ends with thegrasping of the leading end of the strip by the next stand and thebuildup of tension in the strip between the two stands.

In hot rolling the passing of the leading end of the strip can bedetermined by means of the photo-electric cell 27, connected immediatelyafter the stand and reacting to red or infrared light, to effect theswitching over of the switching mechanism 26. The reversal to the highmodulus operating condition can be executed by a second photo-electriccell associated with the following stand or through the load on thepressure cell 29. It is also possible to divert the switching overprocesses only from the pressure cells. For example, as soon as one ofthe pressure cells 29 is under load, the switching mechanism 29 of theassociated stand can be switched to the high modulus condition, whilethe switching mechanism of the next stand in the direction of travel ofthe strip can be switched to the lower modulus condition.

A still further arrangement would be to effect the switching overautomatically by providing the circuits of the mill motors for thestands with measuring devices having terminals, for example, currentrelays capable of triggering the entry switching processes as a functionof the occurrence of maxima or minima current. During the entry of thestrip the drives will operate under an idle condition at the beginning;but then they are loaded when the leading end condition of a strip isgrasped, so that the current used by the motors will be considerablyincreased. When the leading end of the strip enters the following standdue to the tension occurring in the strip, the latter takes charge of apart of the power to be applied so that the current used by the drivingmotors of the preceding stand is again lowered. Therefore, thecorresponding switching mechanism 26 will be switched over to theswitching position corresponding to the lower stand modulus at theearliest during the idling period of the driving motor and at the latestduring the great increase of the current during the entry of the strip,and during the renewed slight decrease of the current it will beswitched over again to the high modulus operating condition. If desired,only the switching over to the low stand modulus can be effected bymeans of current relays or similar devices, while the switching over tothe higher modulus can be effected by the pressure cell 29 or thephoto-electric cell 27 of the following stand.

Turning now to the embodiment illustrated in FIG. 4, in the blockdiagram of FIG. 2, it was represented that for the control devices ofboth housings of the roll stand 1 there is provided a single switchingmechanism 26. In the form of construction of FIG. 4 there is representedthat at least for certain distinct values to be sent to the controldevices of a stand, there are provided two switching elements.

In FIG. 4 the actual value indicators 22 and 32 of both housings of astand are connected to separate control devices 15 and 33, respectively,each assigned to one of the housings of the stand 1. The load to beexpected during the rolling operation to be given either manually or bymeans of data carriers is adjustable through a selsyn 30, whose deliverysignal is sent to both control devices. Likewise, the setting means 21determining the thickness of the roll gap acts upon both controldevices. However, the corresponding desired outputs of the regulatorysignals and the corresponding loads of the housings are fed to thecontrol devices 15 and 33 over special switching mechanisms. Theswitching mechanism 26 presents two inputs for the indicators 24 and 25which correspond to those of FIG. 2 and are provided in common for bothcontrol devices 15 and 33. The outlet of the switching mechanism 26assigned to them is therefore connected with the control device 15 aswell as with the corresponding inlet of the control device 33.

The switching mechanism 26 is completed with further switching mechanism36 jointly connected with it. To inlets of the switching mechanism 36are connected pressure cells 34 and 35 assigned to a different one ofthe housings, indicating the corresponding loads of housings. Theswitching mechanism 36 continuously produces signals representing theexisting loads which are sent to the control devices 15 and 33. Thesecontrol devices are constructed in such a manner that they can effectadjustment movements in dependence of the given roll gap as settingmeans and of the adjustment movement corresponding to the predeterminedelasticity behavior of the stand. The desirable full compensation of theswelling or stretch and, therefore, the ap' proach to an unlimited rigidstand is consciously avoided in the adjustment effected by the controldevices. For practical purposes an additional automatic control systemcan effect correction with a large time constant and be superimposed onthe control. Such a system can monitor the actual gauge by means ofanother measuring device, for example, the monitor 23 of FIG. 2, whichis omitted in FIG. 4 due to its particular diagrammatic representation.

As soon as the strip enters the roll gap there is attained a variationof loads by the pressure cells 34 and 35. The pressure cell 34 feeds asignal to the switching mechanism 26 and switches it over to bring theindicator 24 into effect. The pressure cell 34 is also connected withthe corresponding inlet of the control device 15 and the pressure cell35 is connected with the corresponding inlet of the control device 33.In these switching positions one works with a soft stand and the loadsof the housings are correspondingly transferred to the control device ofthe pertinent housing. In this way the control device can control thepressure in the different piston cylinders 14 associated with thedifferent housings, assuring that the strip will be uniformly reducedduring the period the stand is operating under the soft moduluscondition.

When the strip now enters the following stand, a pressure cell 37associated therewith experiences a considerable load variation, and theswitching mechanism 26 is reversed and also sets back the switchingmechanism 36 similar to what occurs in the aforesaid switching overoperation. In this case the indicator 25 becomes active by means of theswitching mechanism 26 and the rigidity of the housings is increasedthrough a corresponding adjustment of the control devices 15 and 33.Within the switching step 36, the pressure cells 34 and 35 are connectedwith a summation switching device which determines the sum from boththeir individual loads. A signal proportional to one of these sums, thatis to say, a signal corresponding to the arithmetical average of bothhousing loads, is now fed to both inlets running to the controls so thatthey receive the actual value of the loads during the rolling operationand react based upon the arithmetical average of the housing loads aswith customary control devices. FIG. 4 describes also how the switchingover process can be effected through sensors of a given stand and howthe reverse switching can be effected by means of sensors of thefollowing stand.

A further arrangement for the switching over and reverse switching ofthe switching mechanism 26 as well as the switching mechanism 36 isshown in FIG. 2. A photo-electric cell 27 can again be utilized as asensor in this case or, if it is exposed to a large extent to danger offouling by the strip, or if it should not be possible to position such aphoto-electric cell close enough to the roll gap, there can be providedin its place a current relay for the driving motor, a pressure cell 34or a pressure transformer 17. In the given example, the switching overof the switching mechanism 26 will be effected by actuation of thephoto-electric cell 27 wired directly to the switching mechanism 26. Thesame signal can pass a time delay relay 38, only after a time intervaldetermined by it and reach the second or reversing inlet of theswitching mechanism 26. Also, several variants can be introduced withoutdeviating from the invention, e.g., the switching over can be effectedby a considerable load variation of the pressure cell 34, while thereverse switching by means of the photo-electric cell 27 which activatesa current limiting device or similar device in conjunction with a timedelay relay 38. When operating essentially only with current relays, thecurrent impulse resulting in theinitial pass can effect the switchingover to effect a soft stand condition while the slight current dropafter the lowering of load of the drive due to the occurrence of tensionin the strip can be utilized for the reverse switching. For theprotection against the effects of further variations of voltage thecurrent relays can be attached to time relays, which allow the declineof the current only during a determined, relatively short-time intervaland which will release a control signal effecting automatically thereverse switching, if a determinable decline after the predetermiedperiod fails to appear.

In any case the entry of a strip is considerably facilitated and thedesired automatization is accomplished since, during the entryoperation, the corresponding stands are operated with a low standmodulus, that is to say, under a soft modulus condition withconsiderable housing swelling so that the rolls are capable of adaptingthemselves to the strip shape. Consequent lateral deviation of the stripfrom the plane of symmetry of the train is prevented. By means of theability to automatically switch over to a soft mill condition after thepredetermined advance or period of advance, a leading end of the stripnot true to size is limited to a small length and, yet, during theactual rolling process the ideal rolling conditions can be maintained.

In accordance with the provisions of the patent statutes, l haveexplained the principle and operation of my invention and haveillustrated and described what I consider to represent the bestembodiment thereof.

1 claim:

l. A method of operating a rolling mill for rolling strip, said millhaving means for adjusting the roll gap of the mill, the steps of:

passing the leading end of the strip to said mill,

operating the roll gap adjusting means of said mill to cause said millto operate at a low modulus condition during the time the leading endportion of the strip is being rolled by said mill to produce asubstantially uniform reduction across the width of said strip portion,

after the leading end of the strip has been so rolled by said millsubjecting said leading end portion to tension between said mill and atension means, and once said strip tensioning is created operating saidroll gap adjusting means of said mill to permit said mill to be operatedat a higher modulus condition to roll the remaining portion of the stripto a desired longitudinal gauge.

2. A method of operating a rolling mill for rolling strip, said millformed by at least two tandemly arranged mill stands and having meansfor adjusting the roll gaps of the stands, the steps of:

passing the leading end of the strip to a preceding stand of said mill,

operating the roll gap adjusting means of said preceding stand to causesaid stand to operate at a low modulus condition during the time theleading end portion of the strip is being rolled by said stand toproduce a substantially uniform reduction across the width of said stripportion,

after the leading end of the strip has been so rolled by said precedingstand subjecting said leading end portion to tension between saidpreceding stand and a tension means, and

once said strip tensioning is created operating said roll gap adjustingmeans of said preceding stand to permit said preceding stand to beoperated at a higher modulus condition to roll the remaining portion ofthe strip to a desired longitudinal gauge.

3. In a method according to claim 2, characterizing in that saidtensioning is created by a succeeding stand of said mill.

4. In a method according to claim 3, the further step of operating saidroll gap adjusting means of said succeeding stand of said mill to causesaid succeeding stand to operate at a low modulus condition during thetime the leading end portion of the strip is being rolled by saidsucceeding stand to create said tension condition and to produce asubstantially uniform reduction across the width of said strip portion,and

immediately after said rolling commences by said succeeding standchanging the operation of said preceding stand from its low moduluscondition to its higher modulus condition.

5. In a rolling mill for rolling strip,

said mill including means for adjusting the roll gap of I the mill,

a control means for said roll gap adjusting means including means forestablishing at least two different values of mill modulus,

means for causing said roll gap adjusting means to operate said mill ata low modulus condition during the time the leading end portion of thestrip is being rolled to produce a substantially uniform reductionacross the width of said strip portion,

means for subjecting the portion of the strip issuing from the mill totension, and

said control means including means for operating said roll gap adjustingmeans to cause said mill to operate at a higher modulus condition toroll the remaining portion of the strip to a desired longitudinal gauge.

6. In a rolling mill for rolling strip,

said mill made up of at least two mill stands tandemly arranged andincluding means for adjusting the roll gaps of the stands,

a control means for said roll gap adjusting means including means forestablishing at least two different values of mill modulus for eachstand,

means for causing said roll gap adjusting means of a preceding stand ofsaid mill to cause said preceding stand to operate at a low moduluscondition during the time the leading end portion of the strip is beingrolled by said preceding stand to produce a substantially uniformreduction across the width of said strip portion,

means for subjecting the portion of the strip issuing from saidpreceding stand to tension, and

in that said tensioning means comprises a succeeding stand of said mill.

8. In a rolling mill according to claim 7, wherein said control includesmeans for operating said roll gap adjusting means of said succeedingstand of said mill to cause said stand to operate at a low moduluscondition during the time the leading end portion of the strip is beingrolled by said succeeding stand to create said ten- 15 sion conditionand to produce a substantially uniform reduction across the width ofsaid strip portion, and

said control also including means after said rolling commences by saidsucceeding stand to change the operation of said preceding stand fromits low modulus condition to its higher modulus condition.

1. A method of operating a rolling mill for rolling strip, said millhaving means for adjusting the roll gap of the mill, the steps of:passing the leading end of the strip to said mill, operating the rollgap adjusting means of said mill to cause said mill to operate at a lowmodulus condition during the time the leading end portion of the stripis being rolled by said mill to produce a substantially uniformreduction across the width of said strip portion, after the leading endof the strip has been so rolled by said mill subjecting said leading endportion to tension between said mill and a tension means, and once saidstrip tensioning is created operating said roll gap adjusting means ofsaid mill to permit said mill to be operated at a higher moduluscondition to roll the remaining portion of the strip to a desiredlongitudinal gauge.
 2. A method of operating a rolling mill for rollingstrip, said mill formed by at least two tandemly arranged mill standsand having means for adjusting the roll gaps of the stands, the stepsof: passing the leading end of the strip to a preceding stand of saidmill, operating the roll gap adjusting means of said preceding stand tocause said stand to operate at a low modulus condition during the timethe leading end portion of the strip is being rolled by said stand toproduce a substantially uniform reduction across the width of said stripportion, after the leading end of the strip has been so rolled by saidpreceding stand subjecting said leading end portion to tension betweensaid preceding stand and a tension means, and once said strip tensioningis created operating said roll gap adjusting means of said precedingstand to permit said preceding stand to be operated at a higher moduluscondition to roll the remaining portion of the strip to a desiredlongitudinal gauge.
 3. In a method according to claim 2, characterizingin that said tensioning is created by a succeeding stand of said mill.4. In a method according to claim 3, the further step of operating saidroll gap adjusting means of said succeeding stand of said mill to causesaid succeeding stand to operate at a low modulus condition during thetime the leading end portion of the strip is being rolled by saidsucceeding stand to create said tension condition and to produce asubstantially uniform reduction across the width of said strip portion,and immediately after said rolling commences by said succeeding standchanging the operation of said preceding stand from its low moduluscondition to its higher modulus condition.
 5. In a rolling mill forrolling strip, said mill including means for adjusting the roll gap ofthe mill, a control means for said roll gap adjusting means includingmeans for establishing at least two different values of mill modulus,means foR causing said roll gap adjusting means to operate said mill ata low modulus condition during the time the leading end portion of thestrip is being rolled to produce a substantially uniform reductionacross the width of said strip portion, means for subjecting the portionof the strip issuing from the mill to tension, and said control meansincluding means for operating said roll gap adjusting means to causesaid mill to operate at a higher modulus condition to roll the remainingportion of the strip to a desired longitudinal gauge.
 6. In a rollingmill for rolling strip, said mill made up of at least two mill standstandemly arranged and including means for adjusting the roll gaps of thestands, a control means for said roll gap adjusting means includingmeans for establishing at least two different values of mill modulus foreach stand, means for causing said roll gap adjusting means of apreceding stand of said mill to cause said preceding stand to operate ata low modulus condition during the time the leading end portion of thestrip is being rolled by said preceding stand to produce a substantiallyuniform reduction across the width of said strip portion, means forsubjecting the portion of the strip issuing from said preceding stand totension, and said control means including means for operating said rollgap adjusting means of said preceding stand to cause said stand to beoperated at a higher modulus condition to roll the remaining portion ofthe strip to a desired longitudinal gauge.
 7. In a rolling millaccording to claim 6, characterized in that said tensioning meanscomprises a succeeding stand of said mill.
 8. In a rolling millaccording to claim 7, wherein said control includes means for operatingsaid roll gap adjusting means of said succeeding stand of said mill tocause said stand to operate at a low modulus condition during the timethe leading end portion of the strip is being rolled by said succeedingstand to create said tension condition and to produce a substantiallyuniform reduction across the width of said strip portion, and saidcontrol also including means after said rolling commences by saidsucceeding stand to change the operation of said preceding stand fromits low modulus condition to its higher modulus condition.